This post is to provide a set of guidelines for selection as the sources for original devices are drying up and substitutes will have to be sought.
First let's get the definitions clear:
Pre-Drivers are classic RCA410 location. Typically Q11 and Q12 in the PL400 and the PL700B.
Drivers are the classic PL909 location. Typically Q13-Q18 in the PL400 or Q13-Q22 in the PL700B.
Pre-Driver Requirements (less demanding than the Driver requirements):
TO-3 Package
Vce = 200V min.
Slow, Ft less than 1/2 of the output device. Or alternatively 2X it. But not the same. The larger separation, the better. This requirement affects the negative half side of each channel (typically Q12) in order to ensure stability of the quasi-PNP transistor that is formed by the local feedback combination of Q7, Q12 and Q14, 16, 18 (also Q20 and 22 for the PL700B). The positive half side of each channel can use the same Pre-Driver as the Driver as there is no such local feedback condition on the positive half.
Low current gain (this contributes to the low Ft).
Lower noise is better (hardly ever specified, determined by measurement)
Recommended devices: RCA410, MJ410, MJ413, MJ423. possibly 2N6678
Driver Requirements:
TO-3 package
Vce>= 250V
Large SOA, especially ability to sustain more current in the 50msec range at 200V (160V for the PL400) is important. The more current it can withstand, the better. The 21196 is well suited in this regard in that it will safely sustain 1.5A for 50msec at 200V (this is the half sine-wave time duration for a 10Hz signal).
Ft >= 2X the predriver is ideal, the higher the better. Minimum 4MHz is acceptable, higher is better.
Lower noise is better (hardly ever specified, determined by measurement)
The more current gain, the better. The 21196 has hFE between 50-75 at 3A.
Recommended devices: MJ21196, MJ2114, MJ15024
First let's get the definitions clear:
Pre-Drivers are classic RCA410 location. Typically Q11 and Q12 in the PL400 and the PL700B.
Drivers are the classic PL909 location. Typically Q13-Q18 in the PL400 or Q13-Q22 in the PL700B.
Pre-Driver Requirements (less demanding than the Driver requirements):
TO-3 Package
Vce = 200V min.
Slow, Ft less than 1/2 of the output device. Or alternatively 2X it. But not the same. The larger separation, the better. This requirement affects the negative half side of each channel (typically Q12) in order to ensure stability of the quasi-PNP transistor that is formed by the local feedback combination of Q7, Q12 and Q14, 16, 18 (also Q20 and 22 for the PL700B). The positive half side of each channel can use the same Pre-Driver as the Driver as there is no such local feedback condition on the positive half.
Low current gain (this contributes to the low Ft).
Lower noise is better (hardly ever specified, determined by measurement)
Recommended devices: RCA410, MJ410, MJ413, MJ423. possibly 2N6678
Driver Requirements:
TO-3 package
Vce>= 250V
Large SOA, especially ability to sustain more current in the 50msec range at 200V (160V for the PL400) is important. The more current it can withstand, the better. The 21196 is well suited in this regard in that it will safely sustain 1.5A for 50msec at 200V (this is the half sine-wave time duration for a 10Hz signal).
Ft >= 2X the predriver is ideal, the higher the better. Minimum 4MHz is acceptable, higher is better.
Lower noise is better (hardly ever specified, determined by measurement)
The more current gain, the better. The 21196 has hFE between 50-75 at 3A.
Recommended devices: MJ21196, MJ2114, MJ15024
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